Vehicles including automobile have right and left front side frames, sub frames provided in the lower direction of the right and left front side frames, and right and left lateral members extending from the respective rear end portions of the right and left front side frames to the inside in the width direction of the vehicle, as skeleton members on the front portion of the vehicle body.
Moreover, as for the vehicle body front structure in Japanese Laid-Open Patent Publication No. 2013-248982, a fastening nut is provided inside a lateral member, and the fastening nut is screwed with a fastening bolt penetrating the rear end portion of the subframe and the lateral member from the lower direction of the sub frame.
Therefore, a bottom wall of the lateral member functions as a sub frame attaching portion which is fastened to the fastening nut for attaching the sub frame.
Moreover, in the above mentioned structure, the sub frame is attached to the front side frame and the lateral member. This may prevent, when the vehicle is collided from the front direction, the front side frame from bending to absorb the collision energy.
Therefore, as for the vehicle body front structure in Japanese Laid-Open Patent Publication No. 2013-248982, when the vehicle receives the collision load from the front direction, the load is applied, so as to release the attachment of the rear end portion of the sub frame. Namely, the downward load is applied on the fastening nut and the fastening nut falls off from the lateral member.
Furthermore, the lateral member in Japanese Laid-Open Patent Publication No. 2013-248982 has a lateral member main body, and a stiffening member which is layered on and joined to the bottom wall of the lateral member main body. An escape hole portion which has a larger diameter than the fastening nut is formed on the stiffening member.
Therefore, the bottom portion of the lateral member has a region which is formed with a single layer of the lateral member main body, and a region which is formed with two layers made of the lateral member main body and the stiffening member.
Moreover, the region with a single layer has a fastened region which is fastened by a fastener, and an annular weal, portion positioned between the fastened region and the region with the two layers.
As mentioned above, when the downward load is applied on the fastening nut, the weak portion is broken and the fastening nut certainly falls off from the lateral member.